Add option to build the scanned synthesis opcodes

Because these opcodes are non-free according to debian they need to strip
scansyn* from the sources. They also need a patch to remove the opcodes,
that needs to be refreshed on each new csound release.

With this option they can drop the patch and simply specify that scansyn
opcodes are not to be built.

Opcodes/CMakeLists.txt

@@ -16,6 +16,7 @@ option(BUILD_VST4CS_OPCODES "Build the vst4cs opcodes" OFF)
 option(BUILD_EXCITER_OPCODES "Build the exciter opcode" ON)
 option(BUILD_BUCHLA_OPCODES "Build the Buchla filter opcode" ON)
 option(BUILD_PADSYNTH_OPCODES "Build the Padsynth opcode" ON)
+option(BUILD_SCANSYN_OPCODES "Build the scansyn opcodes" ON)
 
 find_package(Boost)
 check_include_file(ladspa.h LADSPA_H)
@@ -101,9 +102,11 @@ if(BUILD_PLATEREV_OPCODES)
    make_plugin(platerev platerev.c m)
 endif()
 
-set(scansyn_SRCS
-    scansyn.c scansynx.c)
-make_plugin(scansyn "${scansyn_SRCS}" m)
+if(BUILD_SCANSYN_OPCODES)
+    set(scansyn_SRCS
+        scansyn.c scansynx.c)
+    make_plugin(scansyn "${scansyn_SRCS}" m)
+endif()
 
 if(UNIX)
     make_plugin(control control.c)